lechoen, Northern has not been rude. She has been very restrained and given excellent advice, despite your drama queen tendencies.
The only really rude poster on this thread has been you, Northern merely defended herself against your rudeness. This is easy to see for anybody who reads this thread from start to finnish in one go.
I second all the excellent parenting advice Norther has given.
I hope you manage to straighten things out with your family.
I had similar issues with the child of my dhs best friend. She would slap my son in the face. And mum would pipe up "awwww, she only does that because she likes him". In the end, I had to tell the girl firmly, to not do it, stop her hand in the action. And tell her parents, "I am sorry, I will not tolerate your child slapping mine, because I dont want him to learn that slapping is ok. Neither should he learn that it is ok that he is slapped". You need to talk to your family about this.
You cannot let your dd learn that it is ok for other children to bite/slap her etc. But you cannot shout at a 19 month old, and then storm out. It is neither here nor there.